This chapter provides an overview of the principles of modern operative fetal intervention. In practice, maternal safety has remained the highest priority in fetal surgery. Some have suggested that pregnant women are a particularly vulnerable group of patients who might have a low threshold to consent to highly invasive fetal therapies, even if the benefits to their unborn children could be small. Preoperative preparation for fetoscopic surgery is done in a fashion similar to that used in open fetal surgery. Fetoscopy offers several distinct advantages when compared with open fetal surgery. The chapter talks about twin-twin transfusion syndrome, airway obstruction, thoracic anomalies, and sacrococcygeal teratoma, congenital diaphragmatic hernia, myelomeningocele, and aortic stenosis. Although most prenatally diagnosed anomalies are best managed after birth, several disorders have predictable, irreversible, and devastating consequences under expectant prenatal management.